Origin of ultra-low friction of boric acid: Role of vapor adsorption

Anthony J. Barthel, Jiawei Luo, Seong H. Kim

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Abstract Boric acid is a lamellar solid lubricant that can give an ultra-low friction coefficient. The origin of this ultra-low friction of boric acid was investigated using tribology and spectroscopy techniques in inert, humid, and organic vapor conditions. It was found that boric acid itself experiences high friction and catastrophic surface wear when rubbed with a stainless steel ball in dry nitrogen or oxygen environments, but it gives very low friction (μ = 0.06) in humid and acetone vapor environments. Short-chain alcohol vapors (ethanol and n-pentanol) did not show these ultra-low friction values. Vibrational spectroscopy indicates that the lubricating vapors do not adsorb on the basal plane of the boric acid crystal but likely adsorb onto the edge sites of the lamella. The alcohol molecules impinging from the gas phase readily react with the boric acid to form a high vapor pressure molecule that desorbs from the surface. The "unlocking" of the high-energy edge sites by adsorbed acetone and water vapor appears to be needed for the lamella to shear along the basal plane direction.

Original languageEnglish (US)
Article number40
JournalTribology Letters
Issue number3
StatePublished - Jun 1 2015

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films


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